About 170 million people log in to Skype’s services every month, though not all of them make calls. Skype users made 207 billion minutes of voice and video calls last year.

Most people use Skype’s free calling services, which has made it difficult for the service to make money since entrepreneurs Niklas Zennstrom and Janus Friis started the company in 2003. An average of about 8.8 million customers per month, or just over 1 percent of the user base, pay to use Skype services.

Skype lost $7 million on revenue of $860 million last year, according to papers that the company has filed since announcing its intentions last summer to launch an initial public offering of stock. The IPO was later put on hold. Skype’s long-term debt, net of cash, was $543,883 at the end of 2010.

Microsoft said Skype will become a new business division headed by Skype CEO Tony Bates, who will report directly to Ballmer.

Although it makes billions from its computer software, Microsoft has been accustomed to losing money on the Internet in a mostly futile attempt to catch up to Google Inc. in the lucrative online search market. Microsoft got so desperate that it made a $47.5 billion bid to buy Yahoo Inc. three years ago, but withdrew the offer after Yahoo balked. Yahoo is now worth about half of what Microsoft offered.

Microsoft would be Skype’s second large-company owner. EBay bought Skype for $2.6 billion in 2005, but its attempt to unite the phone service with its online shopping bazaar never worked out. It wound up selling a 70 percent stake in Skype to a group of investors led by private equity firms Silver Lake and Andreessen Horowitz for $2 billion 18 months ago.